This invention relates to a camshaft driving arrangement for an internal combustion engine and more particularly to an improved tensioner arrangement for such drives.
In four cycle internal combustion engines it is the practice to operate the engine valves from one or more camshafts that are driven in timed relation to the engine crankshaft. The timing drive drives the cam shaft at one half crankshaft speed. Frequently a flexible transmitter such as a belt or chain is employed for this purpose. This is particularly done where the camshaft is journalled in or near the cylinder head where overhead valves are employed.
Since the flexible transmitters commonly employed may change in length during their use and for other reasons it is the common practice to employ a tensioner mechanism on the drive portion of the transmitter for maintaining a constant tension on the transmitter. A pivotally supported tensioner arm is generally employed for this purpose.
An example of a conventional camshaft driving mechanism of this type is shown in Japanese Published Patent Application, publication number Hei 8-121188. As seen therein, the engine comprises an engine body that includes a cylinder block in which a crankshaft is journalled with its rotational axis extending generally horizontally. Camshafts of the valve driving mechanism are supported with the upper part of the engine body and specifically in the cylinder head thereof. A flexible transmitter in the form of a timing chain drives the camshaft in timed relationship with the crankshaft. To maintain the desired tension in the timing chain, a tensioner arm has one end thereof pivoted on the engine body for pivotal movement about an axis that is parallel to the crankshaft axis for engagement with the driving flight of the timing chain. In this way, when the engine is driven, the camshafts operate the intake and exhaust valves in a known manner. The tension arm prevents the timing chain from becoming too slack, thereby preventing the timing chain from vibrating undesirably and producing undesirable noise and making power transmission from the crankshaft to the camshafts smooth.
However, the tension arm is in a free state at the time of assembling or maintenance of the engine and one end of the tension arm may freely swing with its own weight outward of the engine body. Thus the tension arm might interfere with attaching other devices to the engine body. To avoid this it is the practice to provide a temporary stop means to temporarily restrain the movement of the tension arm at the time of assembling or servicing the engine. However, this complicate the jobs of assembling and servicing the engine.
Therefore it is an object of this invention to provide a simple and effective way of preventing unwanted movement of the tensioner arm during assembly and servicing without requiring removable units for this purpose.
This invention is adapted to be embodied in an internal combustion engine comprising an engine body rotatably journaling a crankshaft therein for rotation about a rotational axis. The engine body has an opening at an end thereof spaced from the rotational axis of the crankshaft and adapted to be closed at least in part by a cylinder head detachably connected thereto. The cylinder head journals at least one camshaft for operating at least one valve supported thereon. At least one flexible transmitter drives the camshaft from the crankshaft. A tensioner arm is journalled for pivotal movement by the engine body and has a portion thereof engaged with the flexible transmitter for maintaining a tension therein. The tensioner arm has a portion that extends outwardly beyond the engine body opening. In accordance with the invention, a removable portion of the engine is affixed relative to the engine body and the cylinder head and retained on the engine body when the cylinder head is removed from the engine body. The removable portion is positioned to extend into a portion of the engine body opening from the engine body to engage the tensioner arm and limit its pivotal movement when the cylinder head is removed from the engine body.